NATURE < >!• Kl .SI 'I R VIM >\ 



exceeds many times the volume of O '.. utilized in photosynthesis. 

 A handful of germinating peas or beans placed in a closed jar 

 for a few hours better illustrates the giving off of CO, 1"' 



lure then- i- no green tissue to absorb any of the ( '< K. Plants 

 are often considered unhealthful in sleeping rooms at night be- 

 cause of their exhalation of ( '( )_.. It is well t<» remember that 

 the amount of ( '( >. expired by a plant is small and that a gas 

 jet would furnish more CO a to the air than a window full of 

 plants. 



We are now in a position to understand the importance of 

 photosynthesis and respiration. Photosynthesis keeps the air 

 pure for breathing, decomposes the simple inorganic compounds 



and recombines them into foods which represent a certain amount 



of stored-up energy. Respiration breaks down the f Is into 



products which form the tissues of the plant and sets free the 

 energy necessary for the accomplishment of its growth and move- 

 ments. In the animal .and plant the oxygen decomposes the foods 

 rather slowly and the energy set free is principally manifested as 

 heat .and as the power that enables them to perform their various 

 activities. If the decomposition is sufficiently rapid light as well 

 as heat appears. This is the nature of the reaction when plant 

 tissues, such as wood, are burned. The oxygen s, , rapidly de- 

 Composes the products which compose the wood that heat and 

 light are produced. In our tires we are dealing with the heat and 



sunlight that have been slowly stored up by the plant. 



13. The Third Function of the Leaf, Transpiration. — This 

 function refers to the giving oft" of water by the plant. While 

 other parts of the plan! asdst in transpiration, the leaf is tin 

 principal organ upon which this \er\ considerable work devolves. 

 Water is given off from the plant as a vapor and for this r , 



transpiration i> a more familiar phenomenon than photosynthesis 

 and respiration, where we are dealing with an interchang 

 invisible the vapor from plants growing in a 



window precipitated on the cool window panes in the form of 

 dro|>>. ( in hot Bummer days the leaves of plants droop, litis 

 is because the) have transpired so much water that their cells 

 are no longer distended bj the water, consequently the cells shrink 



